I think I first cut when i was 13-16 I dunno. It happened infrequently as I got older and started dealing with my issues. But the last two years (I'm 23 now) I've had several bad things happen, I'm going threw a divorce, my job is awful, ect. So I've started cutting again.
For me It's a stress thing.

So maybe you have some kind of stress or life altering event?